Background technology
Three-phase grid inverter with LCL filtering, its main circuit and control block diagram are referring to shown in Figure 1, generally include three brachium pontis three-phase inverting circuits based on HF switch, be used for three-phase LCL low pass filter (three-phase symmetrical), three-phase current transmitter and current detection circuit and inverter controller that inversion grid connection connects, wherein inverter controller has comprised current regulator and pwm pulse generator, be output current control when being incorporated into the power networks, with the quality of power supply that guarantees to generate electricity by way of merging two or more grid systems.Because three-phase current is interrelated, three-phase voltage and electric current can be transformed in the dq two-phase synchronous rotating frame from ABC three phase static coordinate system by the synchronously rotating reference frame conversion, so that fundamental signal is done better control.After the synchronously rotating reference frame conversion, LCL filtering three-phase grid inverter output circuit model as shown in Figure 2.Wherein, L
1Be inversion side inductance L
1A, L
1B, L
1CInductance value, L
2Be the grid side inductance L
2A, L
2B, L
2CInductance value, C is filter capacitor C
A, C
B, C
CCapacitance, orthogonal signalling (i
1d, i
1q) and (i
2d, i
2q) be respectively inversion side three pole reactor electric current (i
1A, i
1B, i
1C) and grid side inductive current (i
2A, i
2B, i
2C) through the corresponding amount in dq two phase coordinate systems after the synchronously rotating reference frame conversion, (u
d, u
q), (u
Cd, u
Cq) and (u
Gd, u
Gq) be respectively inversion side three-phase output voltage (u
A, u
B, u
C), filter capacitor voltage (u
CA, u
CB, u
CC) and line voltage (u
GA, u
GB, u
GC) corresponding amount in dq two phase coordinate systems.Owing to carried out rotation transformation, existed complicated coupling between the d phase of system and q phase signals.D, q biphase current are except the amount of being controlled (u
d, u
q) impact, also be subjected to the impact of inversion side inductive current coupling, the coupling of grid side inductive current and capacitance voltage coupling.For d, q biphase current being carried out the accurate control of independence, need to do decoupling zero to system and process.Traditional decoupling zero computing is usually chosen state variable and is directly used in the decoupling zero item from system, exist that the state variable sampling quantity is many, amount of calculation is large, differentiate and disturb the variety of issues such as large, and cost and the control performance of control system all produced adverse influence.As shown in Figure 3, adopt the parallel network reverse control system of state feedback decoupling control need gather the multichannel information about power such as capacitance voltage, inductive current, and differentiate to realize Current Decoupling control.
Summary of the invention
The purpose of this invention is to provide a kind of three-phase grid-connected inverter current decoupling control method based on the synchronously rotating reference frame conversion, under system's output current control requires, coupled relation between each phase electric weight of simplification system and controlled quentity controlled variable, reduce quantity of state number of samples and operand, avoid differentiating, improve the control performance of system.
Three-phase grid-connected inverter current decoupling control method based on the synchronously rotating reference frame conversion of the present invention, comprise the three-phase grid-connected inverter main circuit, three-phase current detection circuit and inverter controller, wherein the three-phase grid-connected inverter main circuit has comprised the three brachium pontis three-phase inverting circuits and the three-phase LCL low pass filter two parts that are connected the inversion grid connection connection based on HF switch, three-phase current detection circuit has comprised and has been used for two groups of current transducers that three-phase LCL low pass filter inversion side inductive current detects and the grid side inductive current detects, inverter controller has comprised the conversion that is tied to dq two-phase synchronous rotating frame from ABC three phase static coordinate, signal errors calculates and proportional integral is regulated, the current regulator of decoupling computing and pwm pulse generator is characterized in that by current regulator three-phase LCL low pass filter inversion side inductor current signal and grid side inductor current signal being passed through respectively two groups of orthogonal signalling i that obtain after the synchronously rotating reference frame conversion
1d, i
1qAnd i
2d, i
2qMake dq two-phase weighted calculation, the dq two-phase weighted average that obtains thus is as feedback signal and the decoupled signals of dq Controlled by Two-Phase ring, the given signal of dq biphase current under the feedback signal of dq Controlled by Two-Phase ring and the synchronous rotating frame is compared, the two-phase error signal of output is inputted respectively dq two-phase proportion integral controller more afterwards, output signal with d phase proportional and integral controller deducts the long-pending of q phase decoupled signals and specific multiplier, the output signal of q phase proportional and integral controller adds the long-pending of d phase decoupled signals and specific multiplier, as the duty cycle of switching signal under the dq two-phase synchronous rotating frame, produce the switch control impuls of three-phase grid-connected inverter by pwm pulse generator, in order to output current wave and the amplitude of controlling combining inverter, wherein, when two groups of orthogonal signalling that obtain after the synchronously rotating reference frame conversion are made dq two-phase weighted calculation, inversion side inductor current signal i
1d, i
1qWeights be LCL low pass filter inversion side inductance value and the ratio of the every phase total inductance of this filter amount, grid side inductor current signal i
2d, i
2qWeights be LCL low pass filter grid side inductance value and the ratio of the every phase total inductance of this filter amount, the above-mentioned specific multiplier that multiplies each other with decoupled signals is the first-harmonic induction reactance of the every phase total inductance of LCL low pass filter and the ratio of three-phase grid-connected inverter dc voltage.
Know-why of the present invention is described as follows:
Analysis is with the combining inverter of three-phase LCL low pass filter, and when the angular frequency of synchronous rotation transformation was ω, the state equation that can obtain parallel network reverse output in the dq synchronous rotating frame was
Two formula additions with in the equation (1) obtain
Two formula additions with in the equation (2) obtain
If with formula (3) and formula (4) both sides respectively divided by
, can get
Introduce following two weighted average variablees,
Adopt above-mentioned weighted average variable substitution formula (5), formula (6), the coupled relation between the dq signal can be simplified, obtain respectively
Formula (9) and formula (10) show that after replacing by above-mentioned reckoning and variable, whenever the be coupled item of three-phase grid inverter output circuit in the state equation of dq coordinate system only has one, and coefficient is constant.This does decoupling zero for next step and controls the condition of providing convenience.
Adopt the HF switch three-phase grid-connected inverter of Duty ratio control, two phase voltage (u are exported in inversion in the dq coordinate system
d, u
q) and inversion control two-phase duty cycle of switching signal (d
d, d
q) relation shown in (11) formula, V wherein
DcBe DC bus-bar voltage.
With following formula substitution formula (9) and formula (10), the relational expression that obtains two-phase weighted average variable and two-phase duty cycle of switching is
(13)
According to formula (12), in order to eliminate the impact of the q phase feedback signal in the d phase current state equation, can in d phase duty ratio, increase a suitable decoupling item.Suppose that the d phase duty ratio increment that is coupled for counteracting q is
, namely
The decoupling item that can get the d phase is:
(15)
Can push away equally to such an extent that the decoupling item of q phase is:
After doing according to the method described above the decoupling processing, formula (12) and formula (13) can be reduced to two independently state equations, are easy to adopt classical control method to carry out the closed loop design of current regulator.Such as the adoption rate integral controller feedback signal error is done closed-loop control.
Method of the present invention has solved the coupled problem that the control of three-phase grid-connected inverter three-phase current exists, make things convenient for the performance optimization of analysis, design and the overall system of control system, enhancing is to the independent control ability of each phase output current, realized the stable output of combining inverter, and made grid-connected system obtain good output current wave.Test shows that in the three-phase grid-connected inverting system of 9kW power, the line voltage distortion factor surpasses under 5% service conditions, and three-phase grid is exported the distortion factor of each phase current all less than 3%, and average distortion measure is 2.91%, and power factor is greater than 0.99.
Control method simple possible of the present invention, the decoupling control method that is used for LCL filtering inverter than traditional has reduced the signal transducers such as filter capacitor voltage or capacitance current.When control loop design, only one of the every phase of calculative decoupling zero item, and be the multiplication operation of variable and constant.Than traditional decoupling control method, adopt this technology can make the control simplicity of design of grid-connected system, implementation method is easy, and systematic function is improved, and has also improved system reliability when reducing the control system cost.
The present invention is applicable to take semiconductor device such as MOSFET, IGBT as power switch, utilize the synchronously rotating reference frame conversion to realize the LCL filtering three-phase grid-connected inverter of current regulation loop control, be used for the various power-supply systems that are incorporated into the power networks such as solar energy, wind-force, fuel cell power generation.
Embodiment
Shown in Figure 1 is main circuit and the control block diagram of combining inverter.It comprises in the three brachium pontis three-phase inverting circuit 1(legends based on HF switch, three-phase inverter is voltage-source type three brachium pontis six switching inverters, employing IGBT is power switch), be used for the LCL low pass filter 2 that inversion grid connection connects operation, be used for two groups of current transducers 3 that three-phase LCL low pass filter inversion side inductive current detects and the grid side inductive current detects, three-phase current detection circuit 4, current regulator 5 and pwm pulse generator 6, wherein current regulator 5(is referring to Fig. 4) comprised electric current weighting average computation 7, error is calculated and proportional and integral controller 8 and decoupling computing 9.
Three-phase grid-connected inverter current decoupling control method based on synchronous rotating frame of the present invention is: adopt two groups of current transducers 3 to detect respectively to flow through LCL low pass filter 2 inversion side inductance L
1A, L
1B, L
1CWith the grid side inductance L
2A, L
2B, L
2CElectric current, give current regulator 5 through three-phase current detection circuit 4 with two groups of current signals, by the synchronously rotating reference frame conversion with the two group orthogonal signalling is of these two groups of current signals under from ABC three phase static coordinate system transformation to dq two-phase rotating coordinate system
1d, i
1qAnd i
2d, i
2qThen calculate mutually weighted average of the 7 d phase weighted averages that obtain these two groups of orthogonal signalling and q by weighted average, with this feedback signal and decoupled signals as dq Controlled by Two-Phase ring, with the feedback signal of dq Controlled by Two-Phase ring respectively with synchronous rotating frame under the mutually given signal of d and the mutually given signal of q compare, the dq two-phase error signal of output is inputted respectively dq two-phase proportion integral controller more afterwards, output signal with d phase proportional and integral controller deducts the long-pending of q phase decoupled signals and specific multiplier, the output signal of q phase proportional and integral controller adds the long-pending of d phase decoupled signals and specific multiplier, as the duty cycle of switching signal under the dq two-phase synchronous rotating frame, produce again the switch control impuls of three-phase grid-connected inverter by pwm pulse generator 6, in order to output current wave and the amplitude of controlling combining inverter, thereby realization is to the closed-loop control of grid-connected current.Wherein, when two groups of orthogonal signalling that obtain after the synchronously rotating reference frame conversion are made dq two-phase weighted calculation, inversion side inductor current signal i
1d, i
1qWeights be inversion side inductance value L
1With every phase total inductance amount (L
1+ L
2) ratio, grid side inductor current signal i
2d, i
2qWeights be grid side inductance value L
2With every phase total inductance amount (L
1+ L
2) ratio, the specific multiplier that multiplies each other with decoupled signals is the first-harmonic induction reactance ω (L of the every phase total inductance of LCL low pass filter
1+ L
2) and three-phase grid-connected inverter dc voltage V
DcThe ratio.
Three-phase grid-connected inverter adopts Current Control PWM mode to move among the present invention, the HF switch frequency component of output current is suppressed under the effect of LCL filter effectively, and the stability of output fundametal compoment and the inhibition of steady-state error and low-frequency harmonics then are decided by the closed-loop control of output current.By the synchronously rotating reference frame conversion, the fundamental current signal becomes DC quantity in the dq coordinate system, and the passing ratio integral control can realize that output current is to the floating tracking of given current signal; By decoupling control method of the present invention, make that dq two is alternate to realize decoupling zero easily, required state feedback variable reduces, and avoided the decoupling zero computing of large amount of complex, thereby for the design optimization of three-phase grid inverse control system provides good basis, so that the control characteristic of grid-connected system is improved and improves.